uboot顶层config.mk分析

#
# (C) Copyright 2000-2006
# Wolfgang Denk, DENX Software Engineering, wd@denx.de.
#
# See file CREDITS for list of people who contributed to this
# project.
#
# This program is free software; you can redistribute it and/or
# modify it under the terms of the GNU General Public License as
# published by the Free Software Foundation; either version 2 of
# the License, or (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston,
# MA 02111-1307 USA
#

#########################################################################

ifneq ($(OBJTREE),$(SRCTREE))
ifeq ($(CURDIR),$(SRCTREE))
dir :=
else
dir := $(subst $(SRCTREE)/,,$(CURDIR))
endif

obj := $(if $(dir),$(OBJTREE)/$(dir)/,$(OBJTREE)/)
src := $(if $(dir),$(SRCTREE)/$(dir)/,$(SRCTREE)/)

$(shell mkdir -p $(obj))
else
obj :=
src :=
endif

# clean the slate ...
PLATFORM_RELFLAGS =
PLATFORM_CPPFLAGS =
PLATFORM_LDFLAGS =

#########################################################################

ifeq ($(HOSTOS),darwin)
HOSTCC = cc
else
HOSTCC = gcc
endif
HOSTCFLAGS = -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer
HOSTSTRIP = strip

#########################################################################
#
# Option checker (courtesy linux kernel) to ensure
# only supported compiler options are used
#
cc-option = $(shell if $(CC) $(CFLAGS) $(1) -S -o /dev/null -xc /dev/null
> /dev/null 2>&1; then echo "$(1)"; else echo "$(2)"; fi ;)

#
# Include the make variables (CC, etc...)

#相关的编译文件
#
AS = $(CROSS_COMPILE)as
LD = $(CROSS_COMPILE)ld
CC = $(CROSS_COMPILE)gcc
CPP = $(CC) -E
AR = $(CROSS_COMPILE)ar
NM = $(CROSS_COMPILE)nm
LDR = $(CROSS_COMPILE)ldr
STRIP = $(CROSS_COMPILE)strip
OBJCOPY = $(CROSS_COMPILE)objcopy
OBJDUMP = $(CROSS_COMPILE)objdump
RANLIB = $(CROSS_COMPILE)RANLIB

#########################################################################

# Load generated board configuration
sinclude $(OBJTREE)/include/autoconf.mk

ifdef ARCH
sinclude $(TOPDIR)/lib_$(ARCH)/config.mk # include architecture dependend rules
endif
ifdef CPU
sinclude $(TOPDIR)/cpu/$(CPU)/config.mk # include CPU specific rules
endif
ifdef SOC
sinclude $(TOPDIR)/cpu/$(CPU)/$(SOC)/config.mk # include SoC specific rules
endif
ifdef VENDOR
BOARDDIR = $(VENDOR)/$(BOARD)
else
BOARDDIR = $(BOARD)
endif
ifdef BOARD
sinclude $(TOPDIR)/board/$(BOARDDIR)/config.mk # include board specific rules
endif

#########################################################################

ifneq (,$(findstring s,$(MAKEFLAGS)))//在$(MAKEFLAGS)查找是否有s字符
ARFLAGS = cr //不太理解这两项的意思
else
ARFLAGS = crv
endif
RELFLAGS= $(PLATFORM_RELFLAGS)
DBGFLAGS= -g # -DDEBUG 调试选项
OPTFLAGS= -Os #-fomit-frame-pointer 优化选项
ifndef LDSCRIPT
#LDSCRIPT := $(TOPDIR)/board/$(BOARDDIR)/u-boot.lds.debug
ifeq ($(CONFIG_NAND_U_BOOT),y)
LDSCRIPT := $(TOPDIR)/board/$(BOARDDIR)/u-boot-nand.lds
else
LDSCRIPT := $(TOPDIR)/board/$(BOARDDIR)/u-boot.lds
endif
endif
OBJCFLAGS += --gap-fill=0xff

gccincdir := $(shell $(CC) -print-file-name=include)

CPPFLAGS := $(DBGFLAGS) $(OPTFLAGS) $(RELFLAGS)
-D__KERNEL__

ifneq ($(BOOT_MEDIA),)
BOOT_MEDIA_MACRO = BOOT_MEDIA_$(shell echo $(BOOT_MEDIA) | tr '[a-z]' '[A-Z]')
CPPFLAGS += -D$(BOOT_MEDIA_MACRO)
endif

ifneq ($(TEXT_BASE),)
CPPFLAGS += -DTEXT_BASE=$(TEXT_BASE)
endif

ifneq ($(OBJTREE),$(SRCTREE))
CPPFLAGS += -I$(OBJTREE)/include2 -I$(OBJTREE)/include
endif

CPPFLAGS += -I$(TOPDIR)/include
CPPFLAGS += -fno-builtin -ffreestanding -nostdinc
-isystem $(gccincdir) -pipe $(PLATFORM_CPPFLAGS)

ifdef BUILD_TAG
CFLAGS := $(CPPFLAGS) -Wall -Wstrict-prototypes
-DBUILD_TAG='"$(BUILD_TAG)"'
else
CFLAGS := $(CPPFLAGS) -Wall -Wstrict-prototypes
endif

CFLAGS += $(call cc-option,-fno-stack-protector)

# avoid trigraph warnings while parsing pci.h (produced by NIOS gcc-2.9)
# this option have to be placed behind -Wall -- that's why it is here
ifeq ($(ARCH),nios)
ifeq ($(findstring 2.9,$(shell $(CC) --version)),2.9)
CFLAGS := $(CPPFLAGS) -Wall -Wno-trigraphs
endif
endif

# $(CPPFLAGS) sets -g, which causes gcc to pass a suitable -g<format>
# option to the assembler.
AFLAGS_DEBUG :=

# turn jbsr into jsr for m68k
ifeq ($(ARCH),m68k)
ifeq ($(findstring 3.4,$(shell $(CC) --version)),3.4)
AFLAGS_DEBUG := -Wa,-gstabs,-S
endif
endif

AFLAGS := $(AFLAGS_DEBUG) -D__ASSEMBLY__ $(CPPFLAGS)

LDFLAGS += -Bstatic -T $(obj)u-boot.lds $(PLATFORM_LDFLAGS)
ifneq ($(TEXT_BASE),)
LDFLAGS += -Ttext $(TEXT_BASE)
endif

# Location of a usable BFD library, where we define "usable" as
# "built for ${HOST}, supports ${TARGET}". Sensible values are
# - When cross-compiling: the root of the cross-environment
# - Linux/ppc (native): /usr
# - NetBSD/ppc (native): you lose ... (must extract these from the
# binutils build directory, plus the native and U-Boot include
# files don't like each other)
#
# So far, this is used only by tools/gdb/Makefile.

ifeq ($(HOSTOS),darwin)
BFD_ROOT_DIR = /usr/local/tools
else
ifeq ($(HOSTARCH),$(ARCH))
# native
BFD_ROOT_DIR = /usr
else
#BFD_ROOT_DIR = /LinuxPPC/CDK # Linux/i386
#BFD_ROOT_DIR = /usr/pkg/cross # NetBSD/i386
BFD_ROOT_DIR = /opt/powerpc
endif
endif

#########################################################################

export HOSTCC HOSTCFLAGS CROSS_COMPILE
AS LD CC CPP AR NM STRIP OBJCOPY OBJDUMP MAKE
export TEXT_BASE PLATFORM_CPPFLAGS PLATFORM_RELFLAGS CPPFLAGS CFLAGS AFLAGS

#########################################################################

# Allow boards to use custom optimize flags on a per dir/file basis
BCURDIR := $(notdir $(CURDIR))
$(obj)%.s: %.S
$(CPP) $(AFLAGS) $(AFLAGS_$(@F)) $(AFLAGS_$(BCURDIR)) -o $@ $<
$(obj)%.o: %.S
$(CC) $(AFLAGS) $(AFLAGS_$(@F)) $(AFLAGS_$(BCURDIR)) -o $@ $< -c
$(obj)%.o: %.c
$(CC) $(CFLAGS) $(CFLAGS_$(@F)) $(CFLAGS_$(BCURDIR)) -o $@ $< -c
$(obj)%.i: %.c
$(CPP) $(CFLAGS) $(CFLAGS_$(@F)) $(CFLAGS_$(BCURDIR)) -o $@ $< -c
$(obj)%.s: %.c
$(CC) $(CFLAGS) $(CFLAGS_$(@F)) $(CFLAGS_$(BCURDIR)) -o $@ $< -c -S

#########################################################################

以下内容摘抄与此处：http://blog.chinaunix.net/uid-11319766-id-3065823.html

uboot的编译选项差不多都写在顶层的config.mk中。下面分析此文件中和编译选项有关的部分。

定义本地编译环境变量：

ifeq ($(HOSTOS),darwin) #如果主机系统为darwin则主机编译器为cc否则为gcc
HOSTCC = cc
else
HOSTCC = gcc
endif
HOSTCFLAGS = -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer
HOSTSTRIP = strip

HOSTCFLAGS变量保存选项：

-Wall : 显示编译中的警告信息

-Wstrict-prototypes : 如果函数的声明或定义没有指出参数类型,编译器就发出警告.

-O2 : 使用O2级别的优化

-fomit-frame-pointer : 对于不需要帧指针的函数,不要在寄存器中保存帧指针

 

下面有一个cc-option变量，此变量保存了一个测试编译选项的命令。其他地方会经常用call函数来调用它，测试编译选项。

cc-option = $(shell if $(CC) $(CFLAGS) $(1) -S -o /dev/null -xc /dev/null
> /dev/null 2>&1; then echo "$(1)"; else echo "$(2)"; fi ;)

这条语句写整齐了如下：

if $(CC) $(CFLAGS) $(1) -S -o /dev/null -xc /dev/null > /dev/null 2>&1;then
 echo "$(1)";
else
 echo "$(2)";
fi;

可以看出这是一条编译命令，变量CC是编译器，变量CFLAGS是编译选项，其中选项

-S：编译后立即结束，不进行汇编等操作。

-o /dev/null : 生成文件到/dev/null，即不生成任何编译结果,要编译的文件也为空。

-xc: 指定按c语言编译

调用此语句如：call cc-option,-a,-b 则如果支持-a选项则返回-a否则返回-b。

 

下面变量是定义各个编译用到的工具，CROSS_COMPILE在顶层Makefile中定义

AS = $(CROSS_COMPILE)as #汇编器
LD = $(CROSS_COMPILE)ld #连接器
CC = $(CROSS_COMPILE)gcc #编译器
CPP = $(CC) -E #预处理
AR = $(CROSS_COMPILE)ar #归档文件
NM = $(CROSS_COMPILE)nm #列出object文件中的符号
LDR = $(CROSS_COMPILE)ldr #默认连接脚本
STRIP = $(CROSS_COMPILE)strip #丢弃目标文件中的符号
OBJCOPY = $(CROSS_COMPILE)objcopy #转换目标文件格式
OBJDUMP = $(CROSS_COMPILE)objdump #反汇编
RANLIB = $(CROSS_COMPILE)RANLIB #产生归档文件索引

 

接下来和编译选项有关的是

 

ifdef ARCH
sinclude $(TOPDIR)/lib_$(ARCH)/config.mk # include architecture dependend rules
endif
ifdef CPU
sinclude $(TOPDIR)/cpu/$(CPU)/config.mk # include CPU specific rules
endif
ifdef SOC
sinclude $(TOPDIR)/cpu/$(CPU)/$(SOC)/config.mk # include SoC specific rules
endif
ifdef VENDOR
BOARDDIR = $(VENDOR)/$(BOARD)
else
BOARDDIR = $(BOARD)
endif
ifdef BOARD
sinclude $(TOPDIR)/board/$(BOARDDIR)/config.mk # include board specific rules
endif

这几行包含了和ARCH,CPU,SOC,BOARD等相关的编译选项的config.mk文件，以lib_arm/config.mk文件为例，此文件中包含这么一句：

PLATFORM_CPPFLAGS += -DCONFIG_ARM -D__ARM__

-D选项是定义的意思，此句即为定义CONFIG_ARM __ARM__这两个值，如果编译C文件则相当于#define CONFIG_ARM这样的语句

还有如下语句：

PLATFORM_CPPFLAGS += $(call cc-option,-marm,)

根据前面提到的cc-option的分析，可以看出，此句测试-marm选项如果被支持的添加进PLATFORM_CPPFLAGS变量，否则则添加空值。后面call函数调用的都是测试一些选择是否能被支持如果支持就添加。此文件中都是尝试添加一切arm体系相关的选项。

此文件最后指定了lds连接文件

LDSCRIPT := $(SRCTREE)/cpu/$(CPU)/u-boot.lds

其他config.mk文件类似。

BOARD相关目录中的config.mk，本例mini2440目录中config.mk则只定义了TEXT_BASE = 0x33F80000，这个变量保存了uboot在内存中运行地址。

 

顶层config.mk中接下来是整合这些编译选项，整理下大致如下,

 

RELFLAGS= $(PLATFORM_RELFLAGS)
DBGFLAGS= -g # -DDEBUG #-g 添加调试信息
OPTFLAGS= -Os #-fomit-frame-pointer
OBJCFLAGS += --gap-fill=0xff #段之间的空隙用0xff填充
gccincdir := $(shell $(CC) -print-file-name=include) #编译器的include路径
CPPFLAGS := $(DBGFLAGS) $(OPTFLAGS) $(RELFLAGS) -D__KERNEL__
 #此变量综合了DBGFLAGS，OPTFLAGS，RELFLAGS编译选项，并定义了__KERBEL__

ifneq ($(TEXT_BASE),)
CPPFLAGS += -DTEXT_BASE=$(TEXT_BASE) #定义了TEXT_BASE变量
endif
CPPFLAGS += -I$(TOPDIR)/include #添加include搜索路径
CPPFLAGS += -fno-builtin -ffreestanding -nostdinc
-isystem $(gccincdir) -pipe $(PLATFORM_CPPFLAGS)
 #-fno-builtin 不接受不是两个下划线的内建函数
 #-ffreestanding 安独立环境编译
 #-nostdinc 不要在标准系统目录中寻找头文件 只在-I指定的目录中搜索
 #-isystem 指定系统目录
 #-pipe 在编译的不同阶段使用管道通讯
 #$(PLATFORM_CPPFLAGS) 添加
CFLAGS := $(CPPFLAGS) -Wall -Wstrict-prototypes
 #-Wstrict-prototypes如果函数的声明或定义没有给出参数类型则警告
CFLAGS += $(call cc-option,-fno-stack-protector)
 #尝试添加-fno-stack-protector选项
AFLAGS := $(AFLAGS_DEBUG) -D__ASSEMBLY__ $(CPPFLAGS)
LDFLAGS += -Bstatic -T $(obj)u-boot.lds $(PLATFORM_LDFLAGS)
 #-Bstatic静态编译 使用u-boot.lds连接描述文件，此文件是LDSCRIPT变量保存的路径复制过来的
ifneq ($(TEXT_BASE),)
LDFLAGS += -Ttext $(TEXT_BASE) #连接运行时的内存地址
endif

 

下面几行规定了各种文件的编译时用到的编译选项：

BCURDIR := $(notdir $(CURDIR))
$(obj)%.s: %.S
 $(CPP) $(AFLAGS) $(AFLAGS_$(@F)) $(AFLAGS_$(BCURDIR)) -o $@ $< //其中$(@F)代表不包含文件路径的目标文件名
$(obj)%.o: %.S
 $(CC) $(AFLAGS) $(AFLAGS_$(@F)) $(AFLAGS_$(BCURDIR)) -o $@ $< -c
$(obj)%.o: %.c
 $(CC) $(CFLAGS) $(CFLAGS_$(@F)) $(CFLAGS_$(BCURDIR)) -o $@ $< -c
$(obj)%.i: %.c
 $(CPP) $(CFLAGS) $(CFLAGS_$(@F)) $(CFLAGS_$(BCURDIR)) -o $@ $< -c
$(obj)%.s: %.c
 $(CC) $(CFLAGS) $(CFLAGS_$(@F)) $(CFLAGS_$(BCURDIR)) -o $@ $< -c -S